Genome composition and pollen viability of Jatropha (Euphorbiaceae) interspecific hybrids by Genomic In Situ Hybridization (GISH)

Interspecific hybridization is required for the development of Jatropha curcas L. improved cultivars, due to its narrow genetic basis. The present study aimed to analyze the parental genomic composition of F(1) and BC(1)F(1) generations derived from interspecific crosses (J. curcas/J. integerrima and J. curcas/J. multifida) by GISH (Genomic In Situ Hybridization), and the meiotic index and pollen viability of F(1) hybrids. In F(1) cells from both hybrids, 11 chromosomes of each parental was observed, as expected, but chromosome rearrangement events could be detected using rDNA chromosome markers, suggesting unbalanced cells. In the BC(1)F(1), both hybrids had 22 chromosomes, suggesting that only n = 11 gametes were viable in the next generation. However, GISH allowed the identification of three and two alien chromosomes in J. curcas//J. integerrima and J. curcas//J. multifida BC(1)F(1) hybrids, respectively, suggesting a preferential transmission of J. curcas chromosomes for both hybrids. Pollen viability in F(1) hybrids derived from J. curcas/J. integerrima crosses were higher (82-83%) than those found for J. curcas/J. multifida (68%), showing post-meiotic problems in these last hybrids, with dyads, triads, polyads, and micronuclei as post-meiosis results. The here presented cytogenetic characterization of interspecific hybrids and their backcross progenies can contribute to the selection of the best genotypes for future assisted breeding of J. curcas.